libpng: Portable Network Graphics (PNG) Reference Library1

PNG (Portable Network Graphics) is an extensible file format for the
lossless, portable, well-compressed storage of raster images. PNG provides
a patent-free replacement for GIF and can also replace many
common uses of TIFF. Indexed-color, grayscale, and truecolor images are
supported, plus an optional alpha channel. Sample depths range from
1 to 16 bits.